Procedure to inhibit or eliminate acid gas generated in process of electrowinning of copper

ABSTRACT

A method for inhibiting or suppressing acid mist generated in a copper electrowinning method comprising adding to electrolyte from which copper is electrowon, a soluble surfactant comprising an extract from the  Quillaja saponaria  Molina tree.

[0001] The present application relates to a method for inhibiting orsuppressing the formation of acid mist above the electrolyte freesurface area in electrowinning (EW) methods, during the recovery ofcopper from acid aqueous solutions generated by leaching (LIX) andSolvent Extraction (SX) methods, in copper hydrometallurgy.Specifically, it relates to a method for inhibiting or suppressing theformation of acid mist above the electrolytic cells for metalelectrowinning, through the use of a surfactant agent. This agent isconstituted by macromolecules of triterpenic saponins, contained in theQuillaja Extract (obtained from the Quillaja saponaria Molina tree),based on carbon, hydrogen and oxygen atoms, and soluble in acidelectrolytes, such as sulfuric acid containing copper in solution.

BACKGROUND

[0002] The recovery of copper from ores by the leaching (LIX), SolventExtraction (SX) and Electrowinning (EW) methods is widely known. SeeU.S. Pat. No. 4,484,990 (Bultman et al.).

[0003] Generally, the oxidized copper ores are dissolved or leached withacid aqueous solutions, thus generating a liquor having copper dissolvedtherein. The aqueous solution (PLS) is contacted with a water-immiscibleorganic solvent containing a copper-selective ion exchange agent. Inthis same step, the organic phase (loaded with copper) and the aqueous(copper-depleted) phase are separated in settler tanks.

[0004] Subsequently, the copper contained in the loaded organic phase isstripped by contacting it with an aqueous solution containing low coppercontent and a high acidity, known as Spent Electrolyte, which is theaqueous output of the EW method. The aqueous solution loaded with copper(coming from the contact with the organic phase) is usually referred toas Rich Electrolyte. The copper solubilized in this electrolyte iselectrochemically recovered as cathode copper by the EW method. Theremaining solution having a low copper content and referred to as SpentElectrolyte, is recirculated to the SX method, such that, in acontinuous and closed circuit operation its main function is to receivecopper from the loaded organic by a mass transfer mechanism.

[0005] The EW method, through the application of an electric current,permits the electrodeposition of elemental copper at the cathodes. As aresult of the electrochemical reactions at the anode, huge amounts ofoxygen gas and, in a much lesser proportion, chlorine gas are generatedat the surface area of the insoluble anodes. The evolution of thesegases forms bubbles at the anode/electrolyte interface, that rise to thesurface of the electrolyte in contact with atmospheric air, where theyburst and entrain strongly acid electrolyte, which is expelled into theair in the form of a fine mist of spray-type droplets that spread abovethe electrolytic cells throughout the EW tankhouse. This acid mistcauses, among others:

[0006] a) a health hazard for tankhouse workers since it affects therespiratory system, eyes and skin, b) corrosion in the metallicstructures of the EW tankhouse, c) damage to the instrument systems, andd) environmental contamination in the surroundings of the SX/EW plant.In order to decrease the deleterious effects of the acid mist generatedin EW plants, various physical and chemical agents are applied.

[0007] Among the most common physical agents, mention should be made tothe use of floating balls, either hollow or dense, made of polypropyleneand of a standard size, that act as a barrier when the bubbles thatgenerate the acid mist burst. Up to three layers of floating balls areplaced on the free surface of the electrolyte.

[0008] In relation to other physical agents employed to decrease theimpact and damage caused by the acid mist, regarding the above mentionedfeatures, there can be recited the disclosures of Chilean InventionPatents Nos. 35,991 and 36,367. These documents describe a coalescerequipment for the gas bubbles generated in one of the electrodesimmersed in a determined electrolyte. To this effect, a baffle isaffixed such that it projects from the electrolyte through the upperzone of the electrode. This baffle is provided with openings to expelthe gas bubbles toward a zone from where they are conveyed byappropriate means. On the other hand, Chilean Invention Patent No.39,673 discloses a device which permits to cover the electrolyte surfacehermetically, and has an opening for the joint evacuation of electrolyteand acid mist.

[0009] The physical agents disclosed for decreasing the acid mist inelectrolytic methods for the recovery of copper have the disadvantage ofacting on the already formed gas bubbles, introducing significantdisadvantages to the EW tankhouse, which may affect operatingparameters, such as, localized corrosion of permanent cathodes,mechanical stability of the electrodes, detachment problems in cathodecopper sheets, etc. Additionally, the costs associated with thesedisadvantages and the operational maintenance thereof, could involvehigh capital investment and an important increase in operating costs.

[0010] Among the chemical agents employed to decrease the impact anddamage caused by the acid mist, regarding the above mentioned features,there can be mentioned the disclosure of Chilean Invention PatentApplication No. 580-95 and U.S. Pat. No. 5,468,353 which describes afluoroaliphatic surfactant supplied to an acid aqueous electrolyte,which decreases the electrolyte surface tension and thereof the size ofthe gas bubbles generated at the anodic electrode. In an EW method, thisdecrease in surface tension stabilizes the bubbles and minimizes thegeneration of acid mist.

[0011] However, the chemical surfactant agents of the fluorochemicaltype have a high unit cost and, in some cases, may affect the phaseseparation times in the SX method, thus generating serious operatingproblems. In that respect, U.S. Pat. No. 5,468,353 suggests operating athigh temperatures.

[0012] Therefore, there arises the need for alternative surfactants toovercome the disadvantages presented in the previous art.

SUMMARY OF THE INVENTION

[0013] The method proposed through the use of chemical surfactantagents, such as the extract from quillaja (Quillaia saponaria Molina),permits to decrease the acid mist in EW methods for the recovery ofcopper acting on the electrolyte surface tension and indirectly on theformation of gas bubbles, in contrast to the physical agents which acton the bursting of the bubbles onto the free surface of the electrolyte.

[0014] Additionally, the alternative surfactant described here has theadvantage over the physical agents that the triterpenic saponin type ofsurfactant used in this invention is soluble in the electrolyte and doesnot interfere with the SX operations. For example it has no impact onthe phase separation steps that follow the extraction, washing andstripping steps.

[0015] With adequate dosages of quillaja extract for decreasing the acidmist to the levels established by the environmental regulations, a “foamblanket” is not necessarily formed on the free surface of theelectrolyte during the EW method. Also, the alternative surfactantdescribed in the present invention reduces acid mist formation withinsignificant foam generation upon the polyethylene spheres arranged onthe electrolyte surface in the electrolytic cells.

[0016] The quillaja extract used in the present invention is derivedfrom the aqueous extraction of Quillaia saponaria Molina, an indigenoustree from Chile. The non-refined aqueous extracts from quillaja contain,among others, triterpenic saponins, sugars, proteins, mucilages,polyphenols and salts. Typical saponin values based on total quillajasolids are 20-45% w/w, typically 20-25% w/w, although the product can beconcentrated to 40-45% solids. Refined aqueous quillaja extract containapproximately 75-80% w/w saponins, based on total solids. Remainingsolids are being minor concentrations of sugars, proteins, mucilages,polyphenols and salts. An analysis of the saponins in Quillaja can befound in Nord et al., Anal. Chim. Acta 446 (2001) 199-209.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 represents a graph of case 3, an industrial scaleapplication example of the invention, wherein (1) represents theaerosols in bank 1, (2) represents the aerosols in bank 2, and (3) thedosage of the additive supplied to EW consisting of Refined QuillajaExtract diluted in Rich Electrolyte.

[0018]FIG. 2 represents a graph of case 3, an industrial scaleapplication example of the invention, wherein (4) represents the dosageof the additive supplied to EW consisting of Refined Quillaja Extractdiluted in Rich Electrolyte, (5) represents the aerosols in bank 4, and(6) represents the aerosols in bank 3.

[0019]FIG. 3 represents a graph of case 3, an industrial scaleapplication example of the invention, wherein (7) represents the dosageof the additive supplied to EW consisting of Refined Quillaja Extractdiluted in Rich Electrolyte, (8) represents the aerosols in bank 6, and(9) represents the aerosols in bank 5.

[0020]FIG. 4 represents a graph of case 2, a semi-industrial scaleapplication example of the invention, wherein (10) represents the dosageof the additive supplied to EW consisting of Refined Quillaja Extractdiluted in Rich Electrolyte, and (11) represents the decrease inaerosols in the EW cell with the use of an additive containing RefinedQuillaja Extract.

[0021]FIG. 5 represents a graph of case 2, a semi-industrial scaleapplication example of the invention, wherein (12) represents thetemperature of the electrolyte in the EW cell, and (13) represents thedecrease in aerosols in the EW cell with the use of an additivecontaining Refined Quillaja Extract.

[0022]FIG. 6 represents a graph of case 2, a semi-industrial scaleapplication example of the invention, wherein (14) represents the copperconcentration, and (15) represents the decrease in aerosols in the EWcell with the use of an additive containing Refined Quillaja Extract.

[0023]FIG. 7 represents a graph of case 1, a pilot scale applicationtest of the invention, wherein (16) represents the dosage of theadditive supplied to EW consisting of Refined Quillaja Extract dilutedin Rich Electrolyte, and (17) represents the aerosols present.

[0024]FIG. 8 represents a graph of case 1, a pilot scale applicationtest of the invention, wherein (18) represents the temperature of theelectrolyte in the cell, and (19) represents the aerosols present, forthe dosage of the additive supplied to EW consisting of Refined QuillajaExtract diluted in Rich Electrolyte.

[0025]FIG. 9 represents a graph of case 1, a pilot scale applicationtest of the invention, wherein (20) represents the copper grade, and(21) represents the aerosols present, for the dosage of the additivesupplied to EW consisting of Refined Quillaja Extract diluted in RichElectrolyte.

[0026]FIG. 10 represents the molecular structure of certain triterpenicsaponins contained in the Refined Quillaja Extracts. In the structure,R¹ represents a saccharide, R² hydrogen or a saccharide, R³ hydrogen, R⁴acyl or a saccharide and R⁴ represents a saccharide. R⁴ is typically amonosaccharide, R^(4′) is typically an oligosaccharide. Acyl istypically fatty acyl.

DETAILED DESCRIPTION OF THE INVENTION

[0027] The method of the present invention for decreasing, inhibiting orsuppressing the formation of acid mist in electrowinning (EW) methods,preferably copper electrowinning, mainly comprises adding refinedquillaj a extract (commercial name Mistop®), obtained from the treeOuillaja saponaria Molina and produced by the company Natural Response,Quilpue, Chile, NR. The addition is made to the EW electrolytic solutionso as to preferably achieve a saponin concentration between 0.3 and 10.0ppm, in the EW electrolyte. This concentration range being sufficient tostabilize the gas bubbles generated at the anode, decreasing, inhibitingor suppressing the acid mist in the copper EW method. The extract may beadded directly to the electrolyte or previously diluted in electrolytebefore addition, e.g., pumped to the electrolyte, e.g., added to EW in adiluted form as an additive to the electrolyte, or else in aconcentrated form directly to the aqueous stream which is continuouslyentering the EW cell.

[0028] During copper SX-EW methods, it is necessary to maintain thedesired surfactant dose in the electrolyte, by supplying the additive,which contains quillaja extract, in a continuous or intermittent form.

[0029] Triterpenic saponins have, as a basic structure, the quillaicacid triterpene, substituted at the 3-C position with a di- ortri-saccharide and at the 28-C position, with an oligosaccharide througha fucose residue, to which are bonded one or two acyl-groups, see FIG.10.

[0030] It is important to mention that the triterpenic saponin type ofsurfactant, e.g., contained in the conveniently highly refined quillaj aextract (commercial name Mistop®) which is added to the electrolyte ofthe EW method, according to the method of the present invention, doesnot interfere on the: a) SX method in relation toextraction/re-extraction kinetics, phase separation time andcharacteristics of the organic phase and washing and stripping steps, b)EW method in relation to the electrolyte in which it is totally solubleand stable, and c) physical and chemical quality of the cathodesproduced.

[0031] Likewise, the surfactant, e.g., contained in the quillaja extractused in the method described in the present invention, decreases thesurface tension of the electrolyte in the EW method, to values below 65Dynes/cm, in the range of 50 to 60 Dynes/cm, at electrolyte temperaturesof @ 30° C. to 50° C., depending on the dosage of the additive suppliedto EW. This is because the surfactant contained in the quillaja extractstabilizes the gas bubbles generated at the anodic electrode during theEW method, to such an extent that the electrolyte trapped on the bubblesurface drains from the bubble, while it bursts slowly when it reachesthe surface of the electrolyte, and does not burst violently as inelectrolytes without a surfactant, thus decreasing the formation of acidmist.

[0032] Without further elaboration, it is believed that one skilled inthe art can, using the preceding description, utilize the presentinvention to its fullest extent. The following preferred specificembodiments are, therefore, to be construed as merely illustrative, andnot limitative of the remainder of the disclosure in any way whatsoever.

[0033] In the foregoing and in the following examples, all temperaturesare set forth uncorrected in degrees Celsius and, all parts andpercentages are by weight, unless otherwise indicated.

EXAMPLES

[0034] The following examples are given for a better understanding ofthe present invention and should not be construed as limiting to thescope and objects of same.

Example 1 Effect of Refined Quillaja Extract on Current Efficiency andCathode Quality. Laboratory Scale Tests

[0035] Laboratory scale copper electrodeposition experiments wereconducted employing industrial electrolyte and small size 750-ml EWelectrolytic cells, and using a determined experimental configuration. Astainless steel cathode (64×120 mm) and two lead anodes (64×20 mm) wereused. The copper was electrowon on both faces of the cathode, which hada total available area of 125.9 em². The chemical composition of theinput and output electrolyte at the electrolytic cell is shown inTable 1. This chemical composition represents typical electrolytes usedin operations of EW methods. TABLE 1 Average chemical composition of theindustrial copper electrowinning electrolyte used in laboratory tests.Copper electrolyte Chemical species EW Input EW Output Cu²⁺ (g/l) 45 35H₂SO₄ (g/l) 165 175 Fe³⁺ (g/l) 1.7 1.7 Co²⁺ (ppm) 140 140 Cl⁻ (ppm) 2727

[0036] In all the experiments, the copper was electrowon during 6 hourswith a constant current density of 300 A/m². The temperature of theelectrolyte in the cell was kept constant at 44° C. by recirculating thesolution through a heat exchanger. The electrolyte was continuouslypumped from the feeding tank to the electrolytic cell in order tomaintain approximately constant its chemical composition, as shown inTable 1. The refined quillaja extract (commercial name Mistop®) wasadded at the desired concentration for the aqueous solution in theelectrolytic cell and in the feeding tank. The current efficiency wascalculated as the increase in the cathode mass and was reproducible indifferent replicated experiments with an experimental error of @±0.5%.

[0037] Table 2 shows the effect of the refined quillaja extract dosage(Mistop®, Natural Response Quilpué, Chile) supplied and the triterpenicsaponin concentration in the electrolyte on the current efficiency andthe morphological characteristics of the copper deposition at theelectrowon cathodes. The morphological characteristics of the copperdeposition were analysed by electron microscopy. The results indicatedthat the addition of refined quillaja extract does not affect thecurrent efficiency or the morphological characteristics of the copperplated out at the cathodes. TABLE 2 Effects of the refined quillajaextract dosage and the triterpenic saponin concentration on currentefficiency and morphological characteristics of the copper cathodes.Refined quillaja Triterpenic extract saponin Morphological dosagesupplied concentration Current characteristics of (ppm) (ppm) Efficiency% copper cathodes 1 0.18 94.3 Smooth, no nodules 3 0.54 94.7 Smooth, nonodules 5 0.90 94.5 Smooth, no nodules 10 1.80 94.3 Smooth, no nodules20 3.60 94.3 Smooth, no nodules

Example 2 Effect of Refined Quillaja Extract on Acid Mist Suppression.Pilot Plant Scale Tests

[0038] The pilot plant physically simulates the SX and EW industrialmethods. The SX method comprises two extraction steps: E-1 and E-2, onewashing step: W-1, and one stripping step: S-1. The organic is the sameused in the industrial plant and is continuously recirculated. The totalinventory of organic is @ 650 litres. The total inventory of electrolyteis @ 3,500 litres. The PLS has the same chemical composition as the PLSused at industrial scale. The refined aqueous solution is discarded andreturned to the leaching heaps. The advance aqueous solution obtainedfrom the stripping step, S-1, is filtered in order to recover theentrained organic and then fed into the EW method. The loaded organicobtained in E-1 is conveyed to a coalescer and subsequently to asettler, in order to recover the entrained aqueous before entering thewashing step. The organic is washed in order to remove any undesirableimpurities from same which might impact the EW method.

[0039] The EW method includes two cells, each one having a width of 0.70m, a length of 1.24 m, and a depth of 1.50 m. Each cell comprises twocathodes and three anodes, similar to those used at the industrialplant, and the electrolyte reaches a level of 1.40 m. The cathodes usedare made of stainless steel having an effective area of 1 m² withlateral PVC insulators, and the anodes are made of Pb—Ca—Sn. Theflowrate of electrolyte to each cell is 14 l/min with an approximateresidence time of 2.26 hours. The harvest cycles vary from 5 to 7 daysand the current density for operation is variable between 250 and 275A/m². The mean temperature of the electrolyte is 45° C. TABLE 3 Averagechemical composition of the EW input copper electrolyte used in pilotplant tests Copper electrolyte Chemical species Copper, Cu2+, g/l 40Sulfuric acid, g/l 180 Cobalt, ppm 200 Total iron, FeT, ppm 800 Fe2+,ppm 40 Manganese, ppm 10 Chlorine, ppm 20 Silica, ppm 50 Aluminum, ppm120

[0040] The additive dosage is supplied to the EW method by using 14liters of rich electrolyte, to which is added the product Mistop®consisting of refined quillaja extract, thus permitting a continuoussupply of additive during 24 hours at a rate of 10 cm³/min via aperistaltic pump, the additive flow being controlled periodically.Surface tensions were measured on the EW electrolyte with a Kruesstensiometer, Model No. 02221. The platinum ring is immersed in anadequate volume of the electrolyte to be measured, @ 30 ml. The ring isslowly raised from the electrolyte by applying an external force. Theforce necessary to completely separate the ring from the electrolytedetermines its surface tension. The highest force reached per unit oflength is the surface tension sought.

[0041] Acid aerosols were measured in the acid mist located above the EWelectrolytic cells, via a MIE Equipment, model pDR-1000, whichdetermines the aerosols values in suspension instantly, as μg or mgaerosols/m³ air. The method comprised measuring during 30 minutes, at anapproximate height of 50 cm above the cathodes ears immersed in theelectrolyte contained in the copper electrowinning cells.

[0042] The main conditions of the EW method which was carried outwithout (Example 1) and with refined quillaja extract (Examples 2 to 5)are shown in Tables 4 and 5 and in the Graph for Case 1. TABLE 4 Mainoperational input variables of the copper EW cells during pilot planttests. Cell Copper ions electrolyte Current Current ElectrolyteConcentration Electrolyte flowrate Intensity, Density, Voltage,temperature in Electrolyte, acidity Test l/min Amper Amper/m² Volt ° C.g/l g/l E1 15.3 1100 275 3.9 50.0 41.4 183.1 E2 13.4 1000 250 4.1 42.039.8 186.8 E3 13.2  854 214 3.9 46.0 36.5 184.2 E4 14.1 1075 269 4.145.0 41.8 179.8 E5 14.1 1000 250 4.0 45.0 39.7 198.5

[0043] TABLE 5 Pilot plant tests. Effect of refined quillaja extractdosage on main electrolyte operational variables and aerosols of thecopper EW method. Electrolyte Refined surface tension Ambient Aerosolquillaja extract Dynes/cm temperature emission, in electrolyte, TestsInput Output ° C. mg/m³ air ppm E1 62 68 20 3.0 0 E2 65 51 20 2.0 5 E352 50 21 1.5 8 E4 52 51 20 0.7 18 E5 43 44 17 0.2 32

Example 3 Effect of Refined Quillaja Extract on Acid Mist Suppression.Semi-Industrial Plant Scale Tests

[0044] The semi-industrial plant consists of 8 cells, 61 anodes and 60cathodes, and was operated at the same industrial plant location. Six ofthe eight cells were arranged in a closed circuit with a stainless steeltank having a capacity of 30 m³ that provides the electrolyte, which maybe commercial or scavenger or a mixture of both, while the 2 remainingcells are left in open circuit. The tank had two heaters in order tomaintain a constant temperature of the electrolyte in the EW cells. Theaverage flowrate of electrolyte to the cells was 14 m³/h. TABLE 6Average operating conditions during semi-industrial copper EW plantscale tests. Flowrate of Copper Electrolyte electrolyte recycledElectrolyte concentration Current flowrate, to industrial plant,temperature, in electrolyte, density, m3/h m3/h ° C. g/l A/m2 72 28 4442 285

[0045] The additive dosage was supplied to the EW from two alternatingindependent plastic tanks, each one having a capacity of 1 m³. Theadditive was prepared with refined quillaj a extract, Mistop®, which wasdiluted in approximately 720 litres of commercial electrolyte, to attaina concentration of 6 ppm of refined quillaja extract in the EWelectrolyte. The additive containing refined quillaja extract diluted inrich electrolyte was prepared every 12 hours using a centrifugal pump,with an additive flowrate containing refined quillaja extract/richelectrolyte of 1 l/min, thus maintaining a continuous 24 h operation inthe semi-industrial plant.

[0046] Surface tension was measured in the EW electrolyte with a Fishertensiometer, model No. 21, using a platinum ring with a circumference of6 mm. The methodology of the measurement was similar to that disclosedin Example 2.

[0047] Acid aerosols were measured in the acid mist via MIE Monitors,models pDR-1000 and pDR-1200. Both models determine the value foraerosols in suspension instantly, as μg or mg of aerosols/m³ air. Thedifference between models pDR-1000 and pDR-1200 is that the latter has apump which guarantees a higher certainty in the measured flow or volume,and permits a bigger air sampling volume for the measurement of acidmist. The technique comprised measuring during 30 minutes at anapproximate height of 1.50 m above the electrolyte free surface in theEW cells.

[0048] Comparative tests were conducted for the measurement of sulfuricacid contained in the acid aerosol determined by MIE, and using themethod of silica-gel tubes and analysis by ion-chromatography. Thevalues obtained by MIE/silica tubes are consistent and corresponding.This means that @ 30 to 40% of the aerosol measured by MIE is acid mistin the form of sulfuric acid.

[0049] The main operating conditions of the EW method without(Example 1) and with refined quillaja extract (Examples 2 to 4) areshown in Table 7 and in the Graph for Case 2.

[0050] Table 7. Effects of the refined quillaja extract dosage on acidmist suppression and operational parameters during semi-industrialcopper EW tests Refined Electrolyte quillaja surface tension Aerosolszone 1, Aerosols Zone 2, extract Dynes/cm Temperature, ° C. mg/m³ airmg/m³ air dosage, EW EW EW Without With Without With Tests ppm InputOutput electrolyte Ambient QE QE QE QE E1 0 51 62 43 22 1.1 — 2.9 — E2 150 49 40 10 1.9 1.6 2.7 2.3 E3 4 62 52 41 20 2.3 1.2 3.4 2.5 E4 6 61 6341 17 0.7 0.4 1.3 0.9

Example 4 Effect of Refined Quillaja Extract on the Suppression of AcidMist. Industrial Scale Application

[0051] The industrial EW tankhouse has a production capacity of 300,000metric tons of fine copper per year, and consists of a building having alength of 493 m and a width of 40 m. This tankhouse uses 984 cells madeof polymeric concrete in a back-to-back arrangement, divided into sixbanks, wherein 128 cells correspond to the scavenger circuit and 856 arecommercial cells. Each cell comprises 61 anodes and 60 cathodes. Thedistance between electrodes is 100 mm, the anodes are made of laminatedLead-Calcium-Tin, the area for cathode deposition is 1 m² and theharvest cycle is 6 to 7 days. The plant has six transformers/rectifierswith a maximum current of 35,000 Amperes.

[0052] The plant uses Kidd technology for permanent cathodes, havingthree detaching machines. As a complement, there are used four Femonttravelling cranes and a chimney system for removing acid mist throughDesom technology design. The automatized travelling cranes areprogrammed to operate linked to the copper cathode detaching machine.They are equipped with laser telemetry, short circuit detectors withinfrared sensors, equipotential bar contact washing, cathode samplingand person's detector.

[0053] The reaped cathodes pass through a rejection station for theproducts that do not meet the required physical quality, while theaccepted cathodes continue toward a sampling station and then to acorrugation station in an alternating manner, wherein finally thepackages are prepared to be loaded onto trucks and sent to port and fromthere to their final destination.

[0054] The average flowrate of rich electrolyte fed into the EW cells is15 m³/h. The effective volume of each cell is 10 m³, resulting in a meanresidence time of the electrolyte in the EW cell of 40 minutes. Thetotal inventory of electrolyte is about 27,000 m³.

[0055] The average operating conditions of the EW method are shown inTable 8. TABLE 8 Average operating conditions of the EW commercial cellsduring supply of quillaja extract to whole plant Discarded ElectrolyteElectrolyte Cu Current Density, Electrolyte electrolyte temperatureconcentration A/m² flowrate m³/h flowrate, ° C. g/l Bank Bank BankScavenger Commercial m³/h Scav. Commer. Scav. Commer Spent 1-2 3-4 5-62355 12097 26.8 38.9 45.2 53.2 40.8 38.7 268 268 275

[0056] In this case, the additive consisting of refined quillaja extractwas not dosed into the plant electrolyte to be supplied to EW. Instead,refined quillaja extract was added directly to the electrolyte whichfeeds the commercial cell circuit via an injection pump to the mainelectrolyte feed line. Surface tension was measured with a Fishertensiometer, model No. 21, using a platinum ring with a circumference of6 cm. The measurement methodology was similar to that disclosed inExample 2.

[0057] Acid aerosols were measured in the acid mist via MIE Monitors,models pDR-1000 and pDR-1200. Both models determine the value foraerosols in suspension instantly, as μg or mg aerosols/m³ air.

[0058] Two central cells of each bank and the middle points of each cellwere selected as measurement points for aerosols. In this way, twovalues were obtained which were averaged to obtain the final value forthe bank.

[0059] The main average operating conditions of the EW method withrefined quillaja extract during the acid mist measurements are shown inTables 8A and 8B and in the Graph for Case 3. TABLE 8A Main operationalinput variables in the copper commercial EW cells during whole planttests. Electrolyte Current density, A/m² Tests temperature, ° C. Bank1-2 Bank 3-4 Bank 5-6 E1 45.5 286 285 288 E2 45.4 275 275 285 E3 45.1288 288 288 E4 44.7 244 244 253

[0060] TABLE 8 B Effects of the refined quillaja extract dosage on acidmist suppression and operational parameters during whole plant copper EWtests. Concentration of refined quillaja Electrolyte extract in surfacetension Aerosols of acid mist above EW Cells electrolyte, Dynes/cm mg/m³air Tests ppm Advance Spent Bank 1 Bank 2 Bank 3 Bank 4 Bank 5 Bank 6 E12.8 60.8 60.6 0.6 1.4 1.3 1.8 1.4 1.5 E2 6.0 61.2 62.3 0.5 1.0 0.9 1.21.3 1.2 E3 8.0 56.8 55.7 0.4 0.8 0.6 1.0 0.6 1.0 E4 8.0 55.7 54.4 0.30.6 0.3 0.7 0.4 0.5

[0061] The entire disclosure[s] of all applications, patents andpublications, cited herein and of corresponding Chile application No.1869-2002, filed Aug. 19, 2002 is incorporated by reference herein.

[0062] The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

[0063] From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. A method for inhibiting or suppressing acid mist generated in acopper electrowinning method comprising adding to electrolyte from whichcopper is electrowon, a soluble surfactant comprising an extract fromthe Quillaja saponaria Molina tree.
 2. The method for inhibiting orsuppressing acid mist according to claim 1, wherein the derivative fromthe Quillaja saponaria Molina tree contains a triterpenic saponin. 3.The method for inhibiting or suppressing acid mist according to claim 2,wherein said quillaja extract contains an heterogeneous mixture oftriterpenic saponins, having a triterpenic core with sugar chains bondedto carbons 3 and 28 of the triterpene.
 4. The method for inhibiting orsuppressing acid mist according to claim 1, wherein the extract is addedin an amount of 0.3 to 10.0 ppm based on triterpenic saponins, to thecopper electrolyte.
 5. The method for inhibiting or suppressing acidmist according to claim 1, wherein the extract decreases surface tensionof the electrolyte to values below 65 dynes/cm at a temperature range ofthe electrolyte of 30° C. to 50° C.
 6. The method for inhibiting orsuppressing acid mist according to claim 3, wherein the extractdecreases surface tension of the electrolyte to values below 65 dynes/cmat a temperature range of the electrolyte of 30° C. to 50° C.
 7. Themethod for inhibiting or suppressing acid mist according to claim 2,wherein the extract contains a triterpenic saponin of the formula

wherein R¹ is a saccharide, R² is H or a saccharide R³ is H R⁴ is acylor a saccharide, and R⁴′ is a saccharide,